I decided to scan a few more. This is sort of an old book, from the beginning of the pandemic. These are $4.00 “Dollarama” sketchbooks, which are great, because they are cheap, and the paper likes watercolour. Brush pen, though, sometimes wicks a bit.
These things claim, however to be “acid free paper,” which is a fib, because they yellow very quickly. So in a few centuries, they might be dust. But I won’t be around either, so what would I care?
Are you using the black hardcoover or the heavier paper books with printed Van Gogh or Turner or Matisse covers? I use the heavier paper books and I love the new larger hardcover sketchbooks. None of mine show evidence of yellowing. I’ve been using them for a few years. Watercolours lose their vibrancy when dry, probably on account of absorption, but I still like the sketchbooks.